Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$87.30	13.556%	$99.1344	$99.13	$99.15	$99.10
Purchase #2	$33.99	6.819%	$36.3078	$36.31	$36.30	$36.30
Purchase #3	$186.28	8.217%	$201.5866	$201.59	$201.60	$201.60
Purchase #4	$206.47	12.181%	$231.6201	$231.62	$231.60	$231.60
Purchase #5	$124.54	5.473%	$131.3561	$131.36	$131.35	$131.40
Purchase #6	$189.38	3.697%	$196.3814	$196.38	$196.40	$196.40
Purchase #7	$75.37	9.359%	$82.4239	$82.42	$82.40	$82.40
7 purchase totals =	$903.33		$978.8103	$978.81	$978.80	$978.80